Fast food is often wrapped in relatively thin paper that is coated so as to mitigate penetration of grease into the structure of the paper and excessive passing through of vapour so as to mitigate loss of opacity and cooling of hot food. Such a wrap paper is typically produced in three major stages. First, a base paper is produced to have a fair opacity. To this end, TiO2 particles are mixed to the pulp. Second, in an off-line process, one side of the base paper is waxed or polyethylene coated. Third, the paper is cut into sheets and packaged into boxes that are suited for end-user's needs.
The coating is made by applying heated wax or polyethylene in an off-line coating station onto a running paper web. The hot coating is in a molten form and thus adheres uniformly to the base paper and forms a barrier layer. The coating layer is relatively thin and light in comparison to the base paper being coated and thus in part cools down by itself to solid state as heat transfers from the coating to the base paper. When the coating is in the solid state, the coated paper is ready to be rolled in or cut into sheets and boxed.
Food wrap papers are produced with different specifications for different needs: hamburger wrap paper, for instance, is typically made of paper having basis weight of 25 g/m2 to 33 g/m2 including a few g/m2 coating. French fries, on the other hand, are typically produced with significantly heavier base paper. Generally, the lighter the base paper, the more prone the paper is for web breaks, holes, wrinkles and other quality defects.
In papermaking, the capacity of paper production lines is constantly being increased as far as possible in order to reduce unit costs and thus to enhance efficiency of the production. The capacity can be effected in a number of ways, such as: increasing production rates (e.g. broader web, faster run speed), reducing down-time (faster grade changes, less web breaks, faster resumption of production after web-breaks) and reducing proportion of production that falls below quality requirements. Paper machines are notoriously expensive production units with which risks are not willingly taken if not absolutely necessary. For example, with the light-weight base paper for hamburger wrap, on-line coating is instantly un-attractive to a skilled person: the paper web is weak and prone for breaking especially when wetted by coating. The off-line coating wax and polyethylene are not suited for on-line coating. In on-line production they would form sticky deposits that accrue and kind of burn onto drying cylinders and rolls. Such stains may ultimately require grinding of cylinders or rolls.
It is an object of the invention to enhance the efficiency of the production of food wrap paper with basis weight of 25.5 g/m2 to 34 g/m2. Another object of the invention is to additionally or alternatively reduce the amount of additives and/or energy needed for production of such food wrap paper. Yet another object of the invention is to additionally or alternatively reduce defects in such food wrap paper.